Precipicio translates to "cliff" or "precipice". It's a dramatic and evocative word that immediately brings to mind danger and a great fall.
In the song, Alejandro Sanz sings, "Tu amor es precipicio, pero daba al mar" (Your love is a cliff, but it led to the sea). He uses this powerful metaphor to describe a love that was both perilous and alluring, hinting at the risk involved but also the vastness and beauty it offered, even if ultimately unattainable.
The whole argument of this song fits into one line, and Alejandro Sanz gets to it fast: "Yo era poesía / Y no sabías leer" ("I was poetry and you didn't know how to read"). It is a spectacular thing to say about an ex, and also a bit much, which is most of the fun. Everything around it is built out of two things that cannot share a room. She is the weather and he is the thing left standing in it: "Tú eras huracán / Demostrando poder / Yo el faro que aguantaba" ("You were a hurricane showing your power, me the lighthouse that held on"). Her love is a drop: "Tu amor es precipicio / Pero daba al mar" ("Your love is a cliff, but it faced the sea"), and the sea turns out to be no kinder, "Tu océano frío / Y yo no sabía nadar" ("Your cold ocean, and I didn't know how to swim").
Under the imagery it is a plain complaint about effort that never got matched. He opens by defining himself as a promise "Que si no se cumple / No se debe hacer" ("that, if it isn't kept, shouldn't be made"), and the thing he waited for was tiny: "Un maldito te quiero / Que jamás llegó" ("a damn 'I love you' that never came"). What stings most is a question of manners rather than betrayal. "Hubieras avisado / Pa' jugar los dos" ("You should have let me know, so we could both play") is a man asking to have been told the rules of a game he was already losing.